The fluid dynamic bearing device refers to a bearing device for supporting a shaft member and a bearing member in freely relatively rotatable and non-contact manners in a radial direction by using a fluid pressure generated through a dynamic pressure action of dynamic pressure generating grooves in a radial bearing gap between the bearing member and the shaft member inserted along an inner periphery of the bearing member. Such a fluid dynamic bearing device is capable of supporting, with high accuracy and quietness, the shaft member relatively rotated at high speed, and hence is suitably used as a bearing for small motors to be mounted to information apparatus, such as a spindle motor for disk drives for HDDs, CD-ROMs, DVD-ROMs, and the like, a polygon scanner motor for laser beam printers, and a fan motor for PCs.
In the small motors to be mounted to the above-mentioned information apparatus, it suffices that the shaft member that is relatively rotated in one direction (forward direction) can be supported. In recent years, there has been studied use of the fluid dynamic bearing device for supporting a shaft member that is relatively rotated in both directions (forward direction and reverse direction) in, for example, servo-motors to be incorporated into machinery equipment or the like and motors to be incorporated into electrical devices of automobiles. However, in a case where the bearing device to be used for supporting the shaft member that is relatively rotated in one direction is used as it is for supporting the shaft member that is relatively rotated in both the directions, when the shaft member is relatively rotated in the reverse direction, a negative pressure may be generated in a part of a region in the radial bearing gap, or an oil film to be formed in the radial bearing gap may be interrupted. Thus, it is difficult to support the shaft member in a desired non-contact manner.
As a countermeasure, as described, for example, in Patent Literature 1 below, there has been proposed a fluid dynamic bearing device in which dynamic pressure generating groove regions (each including a plurality of dynamic pressure generating grooves inclined with respect to an axial direction and arrayed in a circumferential direction) respectively for a forward rotation and a reverse rotation are molded on an inner peripheral surface of a bearing member that forms radial bearing gaps with respect to an outer peripheral surface of a shaft member. With this, the shaft member can be supported in a desired non-contact manner irrespective of whether the shaft member is relatively rotated in the forward direction or the reverse direction.